1. Technical Field
The invention is generally related to the field of creating patterns on substrates. More specifically, the invention relates to patterning substrates with polymeric materials having submicrometer-scale or nanometer-scale features.
2. Background Art
The trend in the semiconductor IC industry is to make devices smaller, faster and cheaper through very high degree of integration. The ever shrinking device geometry has come to a bottleneck due to the limitation of the available lithography technology that is used to define the device minimum feature sizes.
In recent years a number of patterning techniques have been developed to overcome the resolution limit of photolithography. Among these newly developed methods, microcontact printing (μCP) and nanoimprint lithography (NIL) are two high throughput and low cost patterning techniques. Microcontact printing (μCP) typically utilizes a soft polydimethylsiloxane (PDMS) mold or stamp to print self-assembled monolayer patterns using appropriate small molecule inks. The SAM patterns can be transferred to a substrate through special wet etching processes, but are not robust enough to be used as the barrier layer in dry etching. On the other hand, NIL forms a thickness contrast by deforming a thermoplastic polymer film under high pressure at elevated temperature. Because significant polymer flow is required during NIL processes, very high temperature and pressure are needed. After imprinting, a residual polymer layer is left in recessed regions. An additional etching step is required to remove this residual layer before the patterns can be transferred to the substrate. For discussion of μCP and NIL, please see Wilber, J. L., Kumar, A., Kim, E., and Whitesides, G. M., “Microfabrication by Microcontact Printing of Self-Assembled Monolayers”, Adv. Mater., 1994, 6, No.7/8, 600-604; Chou, S. Y., Krauss, P. R., and Renstrom, P. J., “Nanoimprint Lithography”, J. Va. Sci. Technol. B 14(6), November/December 1996, 4129-4133, and U.S. Pat. No. 6,309,580; Granlund, T, Nyberg, T., Roman, L. S., Svensson, M., and Inganas, O., “Patterning of Polymer Light-Emitting Diodes with Soft Lithography”, Adv. Mater. 2000, 12, No. 4, 269-273; and WO 02/086452.
Yet another method, termed reversal imprinting, has been described in the literature by authors including some of the present inventors. During reversal imprinting, a polymer film is spin coated onto a patterned mold and then transferred to a substrate at suitable temperature and pressure. When the mold surface is not planarized after spin coating, the polymer film on the protruded surfaces of the mold can be inked to the substrate. However, because a polymer film continually covers a patterned mold after spin coating, the inked patterns usually display ragged edges due to forced breakage of the polymer film near feature sidewalls. Although using a deep mold coated with a relatively thin coating may alleviate this problem, improvement of the technique would be preferred to reduce edge roughness. See X. D. Huang, L. R. Bao, X. Cheng, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20, 2872 (2002).
Patent Cooperation Treaty published patent application WO 00/70406 describes methods for patterning polymer films. The document describes selective surface treatment of protrusions of a polymeric transfer member with a plasma etch to modify adhesion between the transfer member and the polymer film. In one described method, a polymer film is contacted with protrusions on a plasma-treated transfer member, and portions of the film torn from the whole layer and transferred to a substrate. Very rough edges resulted, and the process can only be practiced with paste-like materials having very low cohesive strength. It is noted that plasticizers are required to be added to the polymer to assist the process, so that the process is not transferring true polymeric ink. It is further noted that the transfer member used was made from a low modulus of elasticity polydimethylsiloxane material, rather than a material having a high modulus of elasticity.
There is a need in many arts, particularly electronics arts, to be able to create sharp, regular or non-regular patterns reproducibly on many substrates, patterns that are not easily removed and that do not change significantly in topography over a wide variety of environmental conditions.